The invention relates to a device for measuring reaction moments and forces on a lever with at least one receptacle for the lever and with at least one carrier, wherein the receptacle is mounted on the carrier so that it can be displaced relative to the carrier in opposite measurement directions, and the device is further provided with at least one stationary sensor for measuring deflections of the lever.
The subject matter of the invention relates to the class of devices for measuring reaction moments and forces on levers. The levers can be aids in measurement arrangements and are formed, for example, as measuring beams. In this case, the measuring beams are components of the measurement device, especially for measuring torques in rotating connections. Alternatively, the levers are sections of shafts or sections on articulated shafts, which are connected in an articulated way to another section via a joint. The reaction forces or reaction moments develop in the device as reactions to torques in rotating connections or in bearings or as reactions to bending moments in joints, when rotating connections or bearings are turned or joints are bent.
The moments of rotating connections are, for example, the torques that develop from friction and/or rolling contact in the rotating connection when two components supported so that they can rotate one on the other or one in the other, for example, the inner ring and the outer ring of a roller bearing, slide one on the other or are supported relative to each other on roller bodies arranged in-between. Here, the lever is turned about the rotational axis at least once 360°. As a rule, the torques of roller bearings should be as low as possible.
In articulated shafts of the drive train of vehicles, the bending moment is a measure for the prevailing play in the joint arrangement. However, for example, in so-called constant-velocity joints, especially in pin universal joints, the play is an evaluation criterion for the function of the articulated shaft arrangement. Unbalanced masses around the rotational axes of the articulated shaft sections can develop due to play that is too great.
The resistance at the bending point of a joint is designated as the bending moment, which is directed opposite the bending of two articulated shaft sections connected to the joint and can be detected and thus can be measured. The bending moment is dependent on the construction of the hinged connection and is comprised, for example, from friction moments and from other resistances of the roller contact at a joint of an articulated shaft of a motor vehicle. In such joints, the value of the bending moment is set at the freedom of play of the joint. The joints are installed intentionally with pre-tensioning. Friction is intentionally set, for example, between the ends of the pin joint and the bases of the universal joint bushings. With the measurement of the bending moment, this resistance can be tested together with other resistances, for example, together with the resistances from the radial roller bearings of the universal joint bushings. For this purpose, a joint section of the articulated shaft arrangement is fixed and the other pivots about one of the axes of the pin joint by an angle up to 90°.
With constant-velocity joints, a hinged connection, which transmits torques and which must allow relative axial movements between the articulated shaft sections, is produced between two articulated shaft sections. For this purpose, the joints usually feature roller bodies, which are guided in raceways and on which the two joint sections roll relative to each other so that they can move in the axial direction and by means of which the joint sections are engaged with each other to transmit torque with a positive fit in the peripheral direction. The friction moments should be as small as possible in this arrangement.
Pin universal joints are hinged connections transmitting torques between two articulated shaft sections without play as much as possible in all directions. In pin universal joints, each of the articulated shaft sections is provided with a joint yoke. The two joint yokes are connected by a universal joint so that they can pivot about two joint axes and are supported usually with low friction as much as possible on the pin of the universal joint via roller bearings. Each of the joint axes corresponds to one of the pin joint axes, which are oriented perpendicular to each other and which cross at the center of the universal joint.
Small play in joint arrangements is important for the function of the articulated shaft. Because the constant-velocity joints should allow axial compensation, the play is positive. Positive plays are air gaps between elements supported one on the other. These plays should be as small as possible, but should also be provided to keep the bending moments small. In contrast, in pin universal joint arrangements, the point and the joint yokes are mounted, as already mentioned above, so that they can move relative to each other, without play, and with pre-tensioning. In order to guarantee freedom of play, the elements are preferably mounted relative to each other with negative play, that is, with pre-tensioning. A measure for the freedom of play or the measure for the pre-tensioning, with which the joint yokes and the pin joint are to be mounted or are assembled with each other is the bending moment, with which the pre-tensioned joint can bend about the respective joint axis.
DE 39 22 194 C1 describes a method and a device of the most general form for measuring bending moments in pin universal joint arrangements. The device is formed by a holder, with which an articulated shaft section is held stationary. The joint yoke of this joint section is oriented in the device so that the other articulated shaft section is driven by the pivot drive so that it can pivot about the joint axes of the pin joint. A bending rod, whose fibers of the outer skin are elongated or compressed as a function of bending direction and resistance of the joint, is arranged between the pivoting joint section and the pivot drive. Expansion measurement strips, with which the expansion of the fibers is detected and converted into corresponding electrical voltage magnitudes, are arranged on the outer skin.
The pivot drive is connected in an articulated way to a radial guide and then via a ball-and-socket joint to the bending rod. The radial guidance can pivot with a pivoting angle of 90° about the rotational axis of the articulated shaft arrangement in the sense of rotation by the pivot drive.
With the method described in DE 39 22 194 C1, in the device counter-acting bending moments about the two joint axes when the moving joint section bends relative to the rigid joint section are measured. For this purpose, the radial guidance is pivoted about the rotational axis on an arc by 90° in the sense of rotation by means of the pivot drive. Here, the counteracting bending moments on the joint axes are first detected in the form of tension magnitudes on the expansion measurement strips of the bending rod. These tension magnitudes are proportional to the bending moments, are recorded, and are selectively converted and displayed legibly in a display device.
DE 41 02 278 A1 shows and describes a device for measuring forces and moments in articulated shaft arrangements with constant-velocity joints. This device has a stationary receptacle, in which one of the joint sections is held rigidly. The other articulated shaft section can pivot relative to the fixed articulated shaft section by the joint. A so-called force-measuring device for force-path measurement, in which the pivoting articulated shaft section is held, is arranged on the pivot axis between the contact of the pivot drive and the joint. The bending moments are converted into deflections (paths) of the receptacle, which are caused in the device by reaction forces to the moments on the bearing.
In the arrangement from DE 41 02 278 A1, an articulated shaft section is held in a receptacle, which is supported so that it can move radially and axially by means of elastic means on carriers. Carriers are fixed in place, for example, on a base plate of the measurement device. The elastic elements should counteract the axial and radial movements and as much as possible have no restoring forces. Force measurement sensors are arranged between the suspended receptacle moving radially and axially and the non-moving carriers.
With force measurement sensors, usually the forces acting on the sensor are not measured directly. These sensors react to the displacement of objects from a starting position with displacements of sensor elements or through their deformation. The displacements and deformation result from forces or from moments. The reactions in the device are first displacements against defined resistances and then the displacement or deformation of sensor elements. In one evaluation device, signals due to deformation are finally converted into force measurement values.
With force sensors, usually compression, shear, and tension forces are all measured. Most force sensors work with at least one spring-elastic body, whose elastic deformation is measured, or they react in a different way, for example, to changes in position using moving elements. Examples for such sensors are tension or compression rods or bending beams or membrane force sensors with expanding measurement strips. In these arrangements, the spring-elastic body is the rod or the bending beam, which is deformed elastically by the force. The force is received in a prescribed direction. The expanding measurement strips are oriented in this direction accordingly. The deformations of the spring-elastic body usually formed from metal are transmitted to the expanding measurement strips, so that these expand and, expressed simply, cause changes in the electrical resistance due to the expansion. The resulting electrical signals are converted into force measurement values.
Alternative force measurement sensors are, for example, piezoelectric force sensors that react to pressure. In a piezoceramic element, a voltage that is proportional to the force is generated due to the force. This voltage can be measured. The use of any suitable force sensor, for example, force sensors with electro-magnetic compensation or other force sensors with distance sensors and current regulation, is also conceivable.
The elastic means, on which the receptacle from DE 41 02 278 A1 is held, are elastically flexible like a hinge only in the pivoting directions, in which the articulated shaft section is pivoted for measuring bending moments. The bending moments are detected at sensors as deflections of the receptacle from an origin or position. The deflections are caused by reaction forces to the moments on the bearing. In the radial and axial direction, the means formed as leaf springs are rigid. Because the axial deflections resulting from the forces are to be measured with this device, the carrier again sits on two other elastic means that can be deflected axially relative to the base plate. These means are also leaf springs, which act in the pivoting directions and are radially rigid but act like a hinge in the axial direction. Sensors, which receive the deflection of the articulated shaft section, are each arranged between fixed carriers and the moving articulated shaft section.
As described in DE 41 02 278 A1, the measurement values are influenced by a coupling equalizing axial movements and by restoring moments of the elastic elements. In addition, the weight of the articulated shaft section is supported on the leaf springs, of which the latter leaf springs also must still receive a part of the weight of the device as a compression or bending load. The leaf springs are strongly dimensioned, in order to withstand these loads without bending and have correspondingly high restoring moments, which can overlap the reaction forces to be measured in the device. Before the beginning of the measurements, complicated calibration processes must be performed, in order to remove the influence of the previously mentioned factors on the measurement results.